This invention is directed to electronic timepiece circuitry for driving a liquid crystal display cell, and, in particular, to detection and control circuitry for detecting the presence or absence of an AC energizing signal applied to the digital display drive circuitry in order to prevent energization of the digital display elements in the absence of a AC signal being detected.
While electronic timepiece digital displays have taken on various forms, one preferred form is a digital display comprised of liquid crystal display cells. Liquid crystal display cells are particularly desirable because of their low current consumption and durability. In order to obtain these benefits, of liquid crystal display cells, it is necessary to effect AC driving of the liquid crystal display cells, and hence, to provide appropriate AC drive circuitry therefor. Nevertheless, because such AC drive circuitry requires the presence of an AC energizing signal produced by the timekeeping circuitry, if, for any reason, the timekeeping circuitry fails to produce a sufficiently high frequency AC energizing signal, the liquid crystal display cells are DC driven, thereby effecting a rapid deterioration of the respective display cells. In fact, such AC driving is selected in order to avoid the rapid deterioration in the liquid crystal display cells that results from DC driving. The instant invention is particularly characterized by detecting and control circuitry for preventing DC driving of liquid crystal display cells in the absence of a AC driving signal being produced by the timekeeping circuitry of the timepiece.